Magnetic Resonance Imaging (MRI) is a recently developed method of evaluation of a subject, such as a human. Anatomical and tissue characterization of the human body are examples of applications of the technique.
In a very broad sense one may compare MRI to standard imaging technologies, such as X-ray and CT scanning. On a fundamental level, however, there is no meaningful comparison, as the basis for each technique is very different. X-ray and CT scanning technologies are well known and will not be summarized here. MRI, briefly, employs the rate of relaxation times of induced magnetization to produce sectional imaging. Many of the risks involved with the use of X-rays, e.g., are not present with the use of MRI, and it can and is used to study all parts of the body.
Of particular interest in the scope of this invention is the examination of longer body parts, such as the spine. In efforts to obtain the best anatomical detail possible, examination using MRI is generally carried out using a solenoid device known as a surface coil. Such devices allow viewing of a particular region of the body, usually not more than 15-25 cm in length. This is much less than the length of the spine, e.g., which is usually between 60 and 100 cm in length. In order to do a complete "sectioning" of a body part such as the spine, the surface coil, which is placed on the examination table upon which the patient rests, must be repositioned at least twice. The repositioning results in increased examination time and patient discomfort. The study obtained may be of inferior quality, since it is quite difficult to reposition the surface coil accurately and "skip overs" may result.
Prior art has all been directed to different, imaging systems, such as X-rays. U.S. Pat. No. 4,232,277 teaches a longitudinal transport carriage which is adapted for use with X-ray film cassettes. The carriage is movable along the length of the patient support platform, and a cassette draw is inserted therein. Clamping jaws then support mount the cassette.
This invention differs from the invention disclosed herein in several respects. First, the patent teaches that cassettes must be inserted and removed. As has been pointed out above, this step almost guarantees that some inaccuracies will result during a series of scans. Continuous examination is not possible. Also, the patent is directed solely to X-rays, which use film, rather than MRI, which uses a surface coil. Finally, as is clear from the patent, the thrust is toward an automatic collimation means, and means for exchange of cassettes via lateral routing.
Additional examples may be found in the patent literature of devices which are used in various X-ray systems, but none of these teach or suggest the present invention. For example, U.S. Pat. No. 4,114,039 teaches an apparatus which is useful in reducing the distance between the patient support table and the roentgenographic device. U.S. Pat. No. 4,196,351 teaches the use of probes in a radiographic detection device which are used to permit different detector placements. Finally, U.S. Pat. No. 3,974,388, teaches a patient support which allows movement of the patient relative to a radiographic apparatus used in preparing sections of a skull.
It will be seen that none of these patents teach or suggest MRI or coil displacement, the major features of this invention.